With the recent increasing demand for reduction in size and weight of electronic equipment, electrochemical devices have been attracting attention. Electrochemical devices are constituted of a variety of constituent materials, and improvement is shown in the respective constituent materials. Of those constituent materials, an electrolytic solution is one of the main materials making up lithium batteries. The electrolytic solution generally comprises an organic solvent, such as propylene carbonate or ethylene carbonate, and an ionic salt, such as lithium fluorophosphate, as a solute, while it depends on matching with positive and negative electrodes. Use of such an electrolytic solution, however, involves many problems in, for example, leakage of liquid, safety, and the like. A polymer having dispersed therein a compound whose ion is easily movable, and a polyelectrolyte layer comprising a crosslinked polymer comprising polyethylene oxide as a main component, have been proposed. However, their performance is insufficient as yet in terms of flexibility at low temperatures or stability. Thus, a satisfactory electrolyte is not yet obtained. It has therefore been demanded to develop an effective polyelectrolyte that overcomes the above problems and will contribute to further advancement of technology.